Featured Science Paper

Ice core records as sea ice proxies: An evaluation from the Weddell Sea region of Antarctica

In a research paper published in the Journal of Geophysical Research in August scientists from the British Antarctic Survey (BAS) describe how they analysed meteorological and ice core data to better understand the crucial role that Antarctic sea ice plays in climate and climate change.

Each winter the sea around Antarctica freezes, forming a salty layer of ice a few metres thick that more than doubles the size of the Antarctic continent. This floating ‘sea ice’ makes the air cold and dry by effectively insulating the ocean so that heat transfer to the atmosphere is reduced and heat from the sun is reflected away.

Whilst historical ship charts and satellite images provide evidence for a rapid decline in Arctic sea ice over recent decades, very little is known about the behaviour of Antarctic sea ice before the satellite era. To make accurate predictions of how Antarctic sea ice will respond to future global change there is a strong need to develop a good ‘proxy’ to reconstruct a picture of the past.

Cores of ice from Antarctica provide an excellent record of the Earth’s past climate. Scientists can measure traces of air and particles that were trapped in snow that fell thousands of years ago and infer what the Earth’s climate was like.

Recent chemical analysis of an ice core from Law Dome found a strong relationship between Methanesulphonic acid (MSA) — a chemical derived from plankton found at the ice edge — and the extent of winter sea ice in the neighbouring region of the Southern Ocean. This was thought to be a promising ‘proxy’ for interpreting ice cores from other parts of the continent.

The BAS researcher Nerilie Abram and her colleagues used statistical techniques to test this relationship on ice cores collected from the Weddell Sea area. In contrast to the Law Dome core she found that the wind conditions that caused greater sea ice formation also tended to blow MSA away from ice core sites around the Weddell Sea.

The result is important because it shows that MSA is not always a reliable ‘proxy’ to interpret past sea ice extent. This demonstrates the need for rigorous examinations of ice core MSA records from other regions around Antarctica in order to develop a robust proxy for Antarctic sea ice.